1. Field of the Invention
The invention relates to bitumen/polymer compositions having an improved stability which is reflected, in particular, by a very good ability to be stored while hot and by excellent mechanical properties. It further relates to the application of the said compositions to the production of surfacings and in particular of road surfacings, of bituminous mixes or alternatively of watertight facings.
2. Background Art
It is known to use bituminous compositions as various surface coatings and in particular as road surface coatings, provided that these compositions have a certain number of essential mechanical qualities.
These mechanical qualities are assessed, in practice, by determining, by standardized tests, a series of mechanical characteristics, the most widely used of which are as follows:
softening temperature (abbreviated to RBT), expressed in 0.degree. C. and determined by the ring-and-ball test defined by NF Standard T 66008,
brittleness point or Fraass point, expressed in 0.degree. C. and determined according to IP Standard 80/53,
penetrability, expressed in 1/10 of an mm and determined according to NF Standard T 66004,
tensile Theological characteristics, determined according to NF Standard T 46002 and comprising the quantities:
yield stress .sigma..sub.y in bars,
elongation at yield stress .epsilon..sub.y in %,
breaking stress .sigma..sub.b in bars,
elongation at break .epsilon..sub.b in %.
In general, conventional bitumens do not simultaneously exhibit all the required qualities and it has been known for a long time that the addition of varied polymers to these conventional bitumens makes it possible to favourably modify the mechanical properties of the said bitumens and to form bitumen/polymer compositions having improved mechanical qualities with respect to those of the bitumens alone.
The polymers capable of being added to the bitumens can be elastomers, such as polyisobutylene, polyisoprene, polybutadiene, polychloroprene, butyl rubber, random ethylene/propylene (EP) copolymers, random ethylene/propylene/diene (EPDM) terpolymers, or polynorbornene, or alternatively plastomers, such as polypropylene, polyethylenes, ethylene/vinyl acetate copolymers, ethylene/methyl acrylate copolymers or ethylene/butyl acrylate copolymers.
Bitumen/polymer compositions based on a bitumen or mixture of bitumens and on one or more polymers of the abovementioned type have a limited stability on storage. Phase separation takes place fairly quickly between the bituminous phase and the polymer phase with, as a consequence, a deterioration in the physicomechanical properties of the said compositions after a relatively short storage time.
It has been found that the incorporation of olefinic polymers carrying epoxy or COOH functional groups in bitumen/polymer compositions composed of a bitumen or mixture of bitumens and of one or more polymers such as mentioned above significantly improved the stability of the said compositions on storage and, by the same token, ensured the maintenance of, indeed even an improvement in, their physicomechanical characteristics.